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Owner’s Manual
for the
BT-350
Bass Amplifier
BT-350
ThunderBass Amplifier
Congratulations!
You are now the proud owner of one of the most advanced bass guitar amplifiers available, the Crate BT-350
ThunderBass amp. This flexible and compact unit combines a tube preamp, 7-band graphic equalizer, chorus, biamp capabilities and 350 watts of power in a rugged and attractive package that can be rack-mounted in only three
spaces. A wide array of front-panel controls along with footswitch options allow you to “tailor” the sound to best
suit your personal needs.
Like all Crate products, your BT-350 ThunderBass amp is Musician Made in the U.S.A., using only the best
components. Extensive testing at many stages in its production, including a final “audition” by a skilled musician,
insures you that your BT-350 ThunderBass amp is the best it can be.
In order to get the best possible performance, please read this manual before you use the amplifier.
.
And thank you for choosing
Contents:
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
The Front Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4, 5
The Rear Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
System Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Using the Biamp Capabilities . . . . . . . . . . . . . . . . . . . . . .8, 9
Some Suggested Settings . . . . . . . . . . . . . . . . . . . . . .10, 11
Technical Specifications . . . . . . . . . . . . . . . . . . . .back cover
CAUTION
ATTENTION
VORSICHT
RISK OF ELECTRIC SHOCK
DO NOT OPEN
RISQUE D'ELECTROCUTION
NE PAS OUVRIR
ELEKTRISCHE SCHLAGGEFAHR
NICHT OFFENEN
CAUTION: TO REDUCE THE RISK OF ELECTRIC SHOCK,
DO NOT REMOVE COVER.
NO USER-SERVICEABLE PARTS INSIDE.
REFER SERVICING TO QUALIFIED SERVICE PERSONNEL.
ATTENTION: POUR REDUIRE D'ELECTROCUTION NE PAS
ENLEVER LE COUVERCLE. AUCUNE PIECE INTERNE N'EST REPRABLE
PAR L'UTILISATEUR. POUR TOUTE REPARATION, S'ADRESSER A UN
TECHNICIEN QUALIFIE.
VORSICHT: ZUR MINIMIERUNG ELEKTRISCHER SCHLAGGEFAHR NICHT
DEN DECKEL ABENHMEN. INTERNE TEILE KONNEN NICHT VOM
BENUTZER GEWARTET WERDEN. DIE WARTUNG IS QUALIFIZIERTEM
WARTUNGSPERSONAL ZU UBERLASSEN.
THIS EQUIPMENT HAS BEEN DESIGNED AND ENGINEERED TO PROVIDE SAFE AND RELIABLE OPERATION. IN ORDER TO PROLONG THE
LIFE OF THE UNIT AND PREVENT ACCIDENTAL DAMAGES OR INJURY, PLEASE FOLLOW THESE PRECAUTIONARY GUIDELINES:
CAUTION: TO REDUCE THE RISK OF ELECTRIC SHOCK, DO NOT OPEN CHASSIS; DO NOT DEFEAT OR REMOVE THE GROUND PIN OF THE
POWER CORD; CONNECT ONLY TO A PROPERLY GROUNDED AC POWER OUTLET.
WARNING: TO REDUCE THE RISK OF FIRE OR ELECTRIC SHOCK, DO NOT EXPOSE THIS EQUIPMENT TO RAIN OR MOISTURE.
CAUTION: NO USER-SERVICEABLE PARTS INSIDE. REFER SERVICING TO QUALIFIED SERVICE PERSONNEL.
CAUTION: OUR AMPLIFIERS ARE CAPABLE OF PRODUCING HIGH SOUND PRESSURE LEVELS. CONTINUED EXPOSURE TO HIGH SOUND
PRESSURE LEVELS CAN CAUSE PERMANENT HEARING IMPAIRMENT OR LOSS. USER CAUTION IS ADVISED AND EAR PROTECTION IS RECOMMENDED IF UNIT IS OPERATED AT HIGH VOLUME.THE CHART BELOW SHOWS THE U.S. GOVERNMENT OCCUPATIONAL SAFETY AND
HEALTH ADMINISTRATION (OSHA) REGULATIONS WHICH WERE IN EFFECT AT THE TIME OF THIS PUBLICATION FOR PERMISSIBLE NOISE
EXPOSURE, PER 29CRF1910, TABLE G-16.
SOUND LEVEL dBA
SLOW RESPONSE
DURATION PER DAY
IN HOURS
SOUND LEVEL dBA
SLOW RESPONSE
DURATION PER DAY
IN HOURS
90
92
95
97
100
8
6
4
3
2
102
105
110
115
1-1/2
1
1/2
1/4 or less
ACCORDING TO OSHA, ANY EXPOSURE IN EXCESS OF THOSE LISTED ABOVE COULD RESULT IN SOME HEARING LOSS.
EXPLANATION OF
GRAPHICAL SYMBOLS:
2
"DANGEROUS VOLTAGE"
= "DANGER HAUTE TENSION"
"GEFAHLICHE SPANNUNG"
"IT IS NECESSARY FOR THE USER TO REFER TO THE INSTRUCTION MANUAL"
= "REFERREZ-VOUS AU MANUAL D'UTILISATION"
"UNBEDINGT IN DER BEDIENUNGSANLEITUNG NACHSCHLAGEN"
BT-350
ThunderBass Amplifier
Introduction:
The Crate BT-350 ThunderBass amp is a high-quality bass guitar amplification system that combines
extremely high power with very desirable features. Each feature and control is discussed in detail in the sections entitled “The Front Panel,” “The Rear Panel” and “Using the Biamp Capabilities.”
Crate offers a heavy-duty three rack space enclosure (Crate model #CR-3) which will house the BT-350
perfectly, providing the extra protection and convenience needed when you take your Crate on the road.
Also available is a five rack space enclosure (Crate model #CR-5) which is ideal for use when the BT-350 is
combined with a second amplifier for biamping.
The BT-350 is equally suited for use in the club, the studio or on the stage. When combined with Crate’s
line of superior bass cabinets, the results are nothing less than phenomenal. (But then, what else would you
expect from Crate?)
Features:
Additional information can be found on the pages indicated.
• Tube Preamp: Adjustable Drive control. Low, Mid and High frequency controls. Low and High Boost
switches. Normal (0dB) and padded (-15dB) input jacks. (page 4)
• Graphic EQ: 7 bands. 40Hz to 10kHz. 12dB cut or boost. Master Level control. Footswitch controllable. LED Indicator. (pages 4 and 5)
• Master Level: Peak (overdrive) LED indicator. Switchable Limiter circuit with LED indicator. (page 4)
• Chorus: Adjustable Depth and Rate controls. Variable cut-off (“Spectrum”) control. (page 5)
• Biamp: Adjustable crossover frequency control. Low-to-high balance control. Independent Line Out
level control. Balanced (XLR) and unbalanced (1/4”) outputs. (pages 5 and 6)
• Internal Amplifier: 350 watts into 4 ohms. 1/4” mono speaker output jacks. Extensive heatsinking.
Detachable AC power cord. (page 6)
• Effects Loop: 1/4” Send and Return jacks. Allows use of external signal processors. Return jack
doubles as input for power amp in Biamp mode. (page 6)
• Musician made in the U.S.A.
• Crate’s exclusive 5-year warranty (U.S. only, – see your dealer in other areas for warranty information)
3
BT-350
ThunderBass Amplifier
The Front Panel:
INPUTS:
1. 0dB INPUT: Connect your bass
here using a shielded instrument cable.
The output signal of your bass will run
full-strength into the amplifier, which is
fine for most basses having passive electronics and/or low-output pickups. If
your bass has active on-board electronics and/or active pickups, use the -15dB
input jack (#2) to avoid overloading the
amp’s input stage.
2. -15dB INPUT: Connect your bass
here if it has active on-board electronics
and/or active pickups. The bass’s output
signal will be attenuated by 15dB to keep
it from overloading the amplifier’s input
stage.
NOTE: Even if your bass has passive
electronics, if the Peak LED (#9) flashes
at seemingly low levels when you’re
plugged into the 0dB input, try using the
-15dB jack instead.
TUBE PRE-AMP section:
3. TUBE DRIVE: This serves as the gain
control for the BT-350’s tube preamp
section, which gives you the natural
compression of a tube amplifier. For the
best compression. adjust the Tube Drive
control as you strike your strings (hard).
Watch the Peak LED (#9): when the
LED starts to flash, you’ve reached a
choice setting for the best signal-to-noise
ratio and “tube feel.”
4. LOW BOOST: Switch on the Low
Boost and you’ll feel a large increase in
the very lowest bass notes, especially
noticeable when you hit the low B string
of a five or six-string bass. This is due to
4
the impressive 8dB of gain added at
20Hz, increasing the deep, “floor-shaking” sounds of your instrument.
5. LOW: Adjust the output level of your
low-bass tones with this control: the center position is “flat” (no boost or cut).
Turning the control to the left reduces the
low frequency output; turning to the
right increases the low frequency output.
The Low control primarily affects the
notes you feel, providing up to 13dB of
boost or cut at 40Hz.
6. MID: Adjust the output level of your
upper-bass tones with this control: the
center position is “flat” (no boost or cut).
Turning the control to the left reduces the
upper-bass output; turning to the right
increases the upper-bass output. The
Mid control provides up to 11dB of
boost or cut at 260Hz, which changes
the “voice” of your instrument’s sound.
By boosting the Mid control you can
make the sound of your bass cut through
the rest of the band, without getting a
whole lot louder.
7. HIGH: Adjust the amount of high-frequency overtones with this control: the
center position is “flat” (no boost or cut).
Turning the control to the left reduces the
high-frequency output; turning to the
right increases the high-frequency output. The High control allows up to 15dB
of boost or cut at 5kHz, which allows you
to adjust the “crispness” of the sound of
your bass. Players looking for a sharp,
slapping sound may tend to want this
control turned up farther than those who
seek a more traditional sound.
8. HIGH BOOST: Turning on the High
Boost greatly enhances the upper-harmonic overtones of your bass, increasing
such subtleties as the sounds of your fingers on the strings or the strings striking
the fretboard. High Boost produces an
additional 10dB of gain at 10kHz, making the “crisp” characteristics of your
bass even more pronounced.
MASTER LEVEL SECTION:
9. PEAK LED: This LED indicator will
light when you’re nearing the highest
desirable level for your input signal and
are in danger of overdriving the preamp’s solid state circuitry. (This can
cause the output of the amplifier to
sound distorted.) To get the maximum
benefit from the BT-350’s tube preamp
section (good, clean sound with the
“feel” of natural tube compression),
adjust the Tube Drive control (#3) until
this LED begins to flash when you’re hitting your strings pretty hard.
10. MASTER LEVEL: This is the BT-350’s
master volume control. The output level
of the amplifier through your main
speakers, the Biamp Outputs and the
Effects Loop Send are simultaneously
adjusted by this control: at the full-left
position there will be no output; rotating
the control to the right increases the volume level.
BT-350
ThunderBass Amplifier
The Front Panel (con’t):
11. LIMIT LED: The BT-350 offers a
special limiting circuit which helps to
keep the output of the amplifier “clean”
when played at extreme volume levels.
When the Limiter is engaged, the Limit
LED will come on as the power amp is
being driven to full output.
12. LIMITER: When a power amplifier
reaches maximum output levels, it may
begin to “clip” its output signal, which
generates potentially speaker-damaging
distortion. The BT-350 has a special
APM (Automatic Power Maximizer) limiting circuit which helps minimize this
problem by monitoring the power amp’s
output signal, keeping it below clipping.
This feature insures you that even as you
push your amplifier to its full 350-watt
output, the sound will remain clean and
pure. To activate the limiter circuit, press
the Limiter switch in until it locks in
place. The limit LED (#11) lights up
when the APM circuit is actually limiting
the signal.
NOTE: The limiter may be defeated,
which allows higher power output, but
there may be more distortion than the
.2% shown in the specifications chart.
BIAMP section:
13. FREQUENCY: This sets the
crossover point when using the BT-350
in the biamp mode (using two power
amplifiers, one for the low frequencies,
one for the highs). Please see the section
entitled “Using the Biamp Capabilities”
on pages 8 and 9 for more details about
biamping.
14. BALANCE: This adjusts the relative
level between the low frequency and the
high frequency biamp output signals.
Please see the section entitled “Using the
Biamp Capabilities” for more details
15. LINE OUT LEVEL: This adjusts the
output level for the Line Outputs jacks
on the rear panel (#31, 32), separately
and independently from the amplifier’s
Master level control (#10). The line out
feature can be used to send a low-level
(pre-amplified) signal to a mixing board,
recorder or external power amp. The
Line Out signal will have the same tone
and Chorus information as the Master
Level (speaker output) signal. Turning
the Line Out Level control to the right
increases the output level; to the left
decreases it.
NOTE: The Line Level signal is preEffects Loop and therefore will not be
affected by any external signal processors connected to the Loop (see #33
and 34).
16. POWER: This heavy-duty rockertype switch is used to turn the amp on in
the “up” position, off when “down.” The
switch lights up when the power is on.
17. FOOTSWITCH: A two-button
footswitch (such as Crate’s CFP-2) can
be plugged in here to give you remote
on/off control of the graphic eq and the
chorus. When connected, the footswitch
overrides the front panel on/off switches
for these features.
NOTE: This is a stereo 1/4” jack: “ring”
controls the chorus, “tip” controls the
eq, and the “sleeve” is ground. Use only
a footswitch equipped with a stereo plug
(such as Crate’s CFP-2).
EQUALIZATION section:
The graphic equalizer can be used in
two different ways: 1: To fine-tune
your sound, make small adjustments
at the desired frequencies and leave
the EQ on for the entire performance;
2: For a completely different sound,
make larger adjustments and only
switch the EQ on when you want the
radical change (such as during bass
solos).
18. LEVEL: This serves as the overall
volume control for the BT-350’s onboard 7-band graphic equalizer, and
only affects the signal when the EQ is on
(see #20). Use this control to adjust the
volume of the equalized signal: pulling
the Level control down from the center
position reduces the volume, pushing it
up from center increases it. The center
detent is “flat” (no increase or decrease
in level).
19. 40Hz – 10kHz: These slide controls
allow you to vary the output at the frequencies shown under each control by
±12dB. The center position of each control is “flat” (no boost or cut): pushing a
control up from center boosts the output
at its given frequency; pulling it down
reduces that frequency. The 40Hz and
100Hz controls affect the lower notes of
your bass, changing how much bass is
felt. 250Hz through 1.6kHz affect the
upper notes, modifying the amount of
“punch” that comes across. 4kHz and
10kHz affect the upper harmonic overtones of your bass, such as the sounds of
your fingers in the strings or the strings
striking the fretboard.
20. ON: When this switch is in, the EQ is
active, and the settings of the controls
affect the sound of your bass.
21. ENABLED LED: This LED will only
light when the EQ is activated, showing
you that the signal will be affected by the
settings of the EQ controls.
CHORUS section:
22. ON: When pushed in, the on-board
Chorus is activated and the signal produced by your bass will have the Chorus
effect applied to it.
23. ENABLED LED: This LED will light
when the Chorus is activated, giving you
a visual sign that the Chorus is functioning.
24. SPECTRUM: (or “crossover:”) This
unique feature allows you to adjust
which frequencies – either the entire
range or only the upper bass tones – are
enhanced by the Chorus effect. In the
fully counter-clockwise position the
entire range (or “spectrum”) will have
the chorus effect. As you rotate the control clockwise you change the roll-off frequency for the Chorus, which allows the
lowest tones to come through “dry”
(without chorus applied). This is
extremely useful for maintaining full lowend impact and definition during live
performances.
25. DEPTH: Adjust the overall amount
of the Chorus effect with this control: to
the left for a little, to the right for a lot.
26. RATE: Adjust the speed of the chorus effect with this control: to the left for
slow, smooth “phasing” sounds, to the
right for faster, “vibrato” sounds.
5
BT-350
ThunderBass Amplifier
The Rear Panel:
27. SPEAKER OUTPUT jacks: Using a
1/4” mono phone plug, connect the output of the BT-350 to your speaker cabinet(s) via these jacks. Be sure to use
heavy gauge speaker cable – not instrument patch cords – for these connections. These jacks are wired in parallel:
when connecting your speakers, keep
the total impedance at or above 4 ohms.
The chart below can help you determine
the total impedance load when connecting various combinations of speakers in
parallel.
SPEAKER
IMPEDANCE
NUMBER OF
SPEAKERS
TOTAL
IMPEDANCE
4 OHMS
1
4 OHMS
8 OHMS
1
8 OHMS
8 OHMS
2
4 OHMS
16 OHMS
2
8 OHMS
16 OHMS
4
4 OHMS
28. AC Line cord: Firmly plug the supplied, heavy-duty grounded power cord
into this receptacle. When in use, be sure
this cord is properly plugged into a safely-wired, grounded 120 volt, 60Hz AC
power outlet. Do not attempt to defeat
the ground connection on this cable!
If your BT-350 was purchased outside of
the United States, see the unit’s rear
panel for its power rating and follow the
above guidelines.
BIAMP OUTPUTS:
29. HIGH OUT: When used in the
biamp mode, this output connects to the
6
high-frequency power amplifier. See the
section entitled “Using the Biamp
Capabilities” on pages 8 and 9 for
details.
30. LOW OUT: When used in the biamp
mode, this output connects to the lowfrequency power amplifier. See the section entitled “Using the Biamp
Capabilities” on pages 8 and 9 for
details.
NOTE: You may access the BT-350’s
internal power amp through the Effect
Return jack (#34), for either the high or
low signal. This is covered in the section
entitled “Using the Biamp Capabilities”
on pages 8 and 9.
LINE OUTPUTS:
31. UNBALANCED: This 1/4” mono
phone jack supplies an unbalanced output signal for connecting to an external
power amplifier. Very short runs (under
20’) to a mixer or recorder having unbalanced inputs can also be made from this
jack; for longer runs use the Balanced
output (#32). The output level at this
jack is adjusted by the Line Out Level
control (#15) on the front panel.
32. BALANCED: This XLR-type connector supplies a balanced signal for connecting to an external mixer, recorder or
power amp which has balanced inputs.
The output is adjusted by the Line Out
Level control (#15). Use the Balanced
output when the distance between the
BT-350 and the mixing console or
recorder is over 20’.
NOTE: The Balanced Output jack is
wired as follows:
PIN 1:
GROUND
PIN 2:
POSITIVE (+)
PIN 3:
NEGATIVE (–)
EFFECTS LOOP:
33. SEND: When using an external signal processor with the BT-350, connect
a shielded cable between the Send jack
of the amplifier and the input of the
effects unit. This “sends” the pre-amplified bass signal to the device for processing.
34. RETURN: When using an external
signal processor, connect a shielded
cable between the output of the effects
unit and the Return jack of the amplifier.
This “returns” the processed bass signal
to the BT-350’s internal amplifier.
BT-350
ThunderBass Amplifier
System Block Diagram:
7
BT-350
ThunderBass Amplifier
Using the Biamp Capabilities:
Your BT-350 can be used along with an additional power amplifier, to “biamp” your system: that is, using two amplifier/speaker combinations to share the task of reproducing the full range of your bass. Due to increased efficiencies, the
combined output may sound cleaner and more powerful than that of a single-amped system, especially during high-volume, live performances.
Using the BT-350 as the low-frequency power amplifier:
In the biamp configuration shown below, the BT-350 serves as the system preamp, biamp crossover, and low-frequency power amplifier. A second power amp of 75 to 200 watts (such as the Crate model SPA-200) may be used to
amplify the upper frequencies. The crossover frequency (that point where one amplifier ends and the other amp takes
over) is set by adjusting the BT-350’s Biamp Frequency control (#13).
To connect the unit for biamp operation using the BT-350 as the low-frequency power amp, refer to the diagram below:
1
Connect a shielded cable from the BT-350’s Biamp HIGH OUT jack and the input of the amplifier which
will be used for the upper frequencies.
2
Connect a shielded cable from the BT-350’s Biamp LOW OUT jack and its Effects Loop RETURN jack.
3
Connect the Speaker Outputs of your high-frequency power amp to the speaker cabinet(s) that will be
used to reproduce the upper frequencies. (10” or 12” drivers work well for this.)
4
Connect the Speaker Outputs of the BT-350 to the speaker cabinet(s) that will be used to reproduce the
low bass notes. (Woofers in the 15” to 18” range work well for these low notes.)
Use the BT-350’s Balance control (#14) to adjust the relative level of lows to highs: to increase the level of low frequencies in the mix, rotate the Balance control to the left (towards “LOW”). To increase the amount of highs in the mix,
rotate the control to the right (towards “HIGH”).
8
BT-350
ThunderBass Amplifier
Using the Biamp Capabilities (con’t):
Using the BT-350 as the high-frequency power amplifier:
In the biamp configuration shown below, the BT-350 serves as the system preamp, biamp crossover, and high-frequency power amplifier. A second power amp of 200 to 500 watts may be used to amplify the low frequencies. The
crossover frequency (that point where one amplifier ends and the other amp takes over) is set by adjusting the BT-350’s
Biamp Frequency control (#13).
To connect the unit for biamp operation using the BT-350 as the high-frequency power amp, refer to the diagram below:
5
Connect a shielded cable from the BT-350’s Biamp LOW OUT jack and the input of the amplifier which
will be used for the low frequencies.
6
Connect a shielded cable from the BT-350’s Biamp HIGH OUT jack and its Effects Loop RETURN jack.
7
Connect the Speaker Outputs of your low-frequency power amp to the speaker cabinet(s) that will be
used to reproduce the low bass notes. (Woofers in the 15” to 18” range work well for these low notes.)
8
Connect the Speaker Outputs of the BT-350 to the speaker cabinet(s) that will be used to reproduce the
upper bass notes. (10” or 12” drivers work well for this.)
Use the BT-350’s Balance control (#14) to adjust the relative level of lows to highs: to increase the level of low frequencies in the mix, rotate the Balance control to the left (towards “LOW”). To increase the amount of highs in the mix,
rotate the control to the right (towards “HIGH”).
9
BT-350
ThunderBass Amplifier
Some Suggested Settings:
ROCK:
Biamp and Chorus controls optional. You can crank the Tube Drive even more for distortion; if you do, back off the
EQ level.
JAZZ:
This will produce a very smooth sound with a minimum of percussive tones.
10
BT-350
ThunderBass Amplifier
Some Suggested Settings:
COUNTRY:
Increasing the EQ Level produces more clean volume. Set the Master Level to taste.
FUNK “POPPING”:
Chorus is a great effect with this setting.
11
BT-350
ThunderBass Amplifier
Technical Specifications:
Output Power Rating
350 watts @ 0.2% THD, 4 ohm load – 120VAC
200 watts @ 0.2% THD, 8 ohm load – 120VAC
Gain @ 1kHz
61dB, tones at “5”
Tone Control Range
Low Boost
Low
Mid
High
High Boost
+8dB @ 20Hz
±13dB @ 40Hz
±11dB @ 260Hz
±15dB @ 5kHz
+10dB @ 10kHz
Graphic EQ Level
+8dB, -10dB
Graphic EQ Range
±12dB @ 40Hz, 100Hz, 250Hz, 625Hz, 1.6kHz, 4kHz, 10kHz
Signal to Noise Ratio
84dB typical
Input Impedance
0dB input: 1M ohm
-15dB input: 122k ohm
Maximum Signal Level Accepted
0dB input: 2.5V peak to peak
-15dB input: 14V peak to peak
Tube Type:
12AX7 (preamp)
Effects Loop Level
1V RMS for full power output
Power Requirements
Domestic
Export
120VAC, 60 Hz, 10A
240VAC, 50 Hz, 5A
Size and Weight
5.25”H x 19”W x 15.75”D, 36 lbs.
CRATE continually develops new products, as well as improves existing ones. For this reason,
specifications and information in this manual are subject to change without notice.
CRATE/SLM ELECTRONICS, A DIVISION OF ST. LOUIS MUSIC, 1400 FERGUSON AVENUE, ST. LOUIS, MO 63133
47-599-02 • 02-96